For example, a vehicle-mounted video apparatus that electrically moves a display section or changes the orientation thereof includes a gear mechanism with torque limiter in order to protect a user from being hurt in the event that the user gets a finger caught in the display section, and to protect components constituting the mechanism from being damaged by an external force. Gear mechanisms with torque limiter include a gear mechanism arranged such that a felt member is gripped or held between a large diameter gear and a small diameter gear disposed coaxially with each other, the felt member is rotated integrally with each gear, and rotation of one gear is transmitted to the other by the frictional force of the felt member. In such a gear mechanism with torque limiter, when a rotation torque is transmitted from one gear to the other gear, if an excessive load is imposed on the other gear, the felt member rotating together with the one gear slips on the contact face thereof between the felt member and the other gear, and thereby the felt member restricts the transmission of the torque to the other gear.
Further, gear mechanisms with torque limiter include a gear mechanism arranged such that a coaxially disposed large diameter gear and small diameter gear each have elongated holes provided therein, a rigid ball is disposed within each of those elongated holes, and the rigid ball is sandwichedly held with two metallic friction plates, thus enabling the transmission of a high torque (See for example, Patent Document 1: JP-A-2004-360809, pp. 5-8, FIGS. 1-5).
Since conventional gear mechanisms having a torque limiter are arranged as described above, when a large drive torque is required by upsizing of a display section or the like, it is necessary to increase the force for gripping a felt member therebetween in the gear mechanism with torque limiter. However, as the force for gripping the felt member therebetween is increased, the thickness of the felt member is gradually reduced. Thus, convexities provided on a gear in order to stabilize the occurrence of the felt member slippling can pierce the felt member causing the tip of the convexity to come in contact with the other gear, which leads to instability of the restricting operation of the gear mechanism based on a predetermined torque limit value. Moreover, abnormal noise is generated by contact between those portions. Also, there is a problem that the application of metallic rigid balls and metallic friction plates to the gear mechanism with torque limiter makes it difficult to downsize and reduce the weight of the mechanism.
The present invention has been made to solve the above-mentioned problems. An object of the present invention is to provide a gear mechanism with torque limiter wherein even if deterioration due to aging, such as a reduction in the thickness of the felt member, occurs, slippage still occurs when a torque greater than or equal to a predetermined torque value is applied thereto, and also the abnormal noise is not produced.